Laser Micromachining System Research Articles

Generic software tool for counteracting the dynamics effects of optical beam delivery systems

Laser micro-machining is a promising manufacturing solution for fabricating complex micro-engineering products in wide range of materials that incorporate different multi-scale functional features. Optical beam deflector systems are key components in laser micro-machining systems, and they are one of the main factors determining the processing speed and hence machining throughput. However, their performance is speed dependent and the negative dynamics effects have a direct impact on the laser micro-machining accuracy, repeatability and reproducibility. This article presents a generic software solution for minimising these negative dynamics effects, thus improving significantly the laser machining performance across the full range of available processing speeds. In particular, these improvements are achieved by introducing machine-specific compensations in machining vectors to counteract beam deflectors’ inertia regardless of their directions, length and set process speed. An empirical model was developed to obtain data about the actual dynamic response of the beam deflection system across the full range of available processing speeds, and then based on these data, the proposed generic software was implemented into a stand-alone ‘adaptive’ postprocessor. The generation of machine executable part programs is automated, and it is only necessary for the user to enter the selected scanning speeds and beam diameters. Experimental validation was conducted to demonstrate the capability of the proposed software tool. The results demonstrate that substantial improvements can be obtained in machining quality by maintaining a constant pulse distance throughout the machining operations, while the dimensional accuracy is maintained across the available processing speeds without sacrificing the machining efficiency.

An investigation of accuracy, repeatability and reproducibility of laser micromachining systems

Component technologies of laser micro machining systems are key factors affecting their overall performance. The effects of these technologies on accuracy, repeatability and reproducibility (ARR) in different implementations of such systems have to be investigated to quantify their contributions to the overall processing uncertainty, especially those with the highest impact on beam delivery sub-systems. The aim of this research was to evaluate the capabilities of state-of-the-art machining platforms that were specially designed and implemented for laser micro structuring and texturing. An empirical comparative study was conducted to quantify the effects of key component technologies on ARR of four state-of-the-art systems. In particular, the capabilities of the optical and mechanical axes were investigated when they were utilised separately or in combination for precision laser machining. Conclusions are made about the positional accuracy of the mechanical and optical axes and the importance of their proper calibration on the systems’ overall performance is discussed. It is shown that the laser machining platforms can achieve repeatability and reproducibility better than 2μm and 6μm, respectively.

Direct CO_2 laser-based generation of holographic structures on the surface of glass

A customized CO(2) laser micromachining system was used for the generation of phase holographic structures directly on the surface of fused silica (HPFS(®)7980 Corning) and Borofloat(®)33 (Schott AG) glass. This process used pulses of duration 10µs and nominal wavelength 10.59µm. The pulse energy delivered to the glass workpiece was controlled by an acousto-optic modulator. The laser-generated structures were optically smooth and crack free. We demonstrated their use as diffractive optical elements (DOEs), which could be exploited as anti-counterfeiting markings embedded into valuable glass-made components and products.

Generic integration tools for reconfigurable laser micromachining systems

Laser micro-machining (LMM) is an attractive manufacturing process due to its intrinsic machining characteristics such as such as non-contact processing and capabilities to machine complex free-form surfaces in a wide range of materials. Nevertheless, state-of-art LMM platforms still do not offer the repeatability, reproducibility and operability of conventional machining centres, e.g. the flexibility to realise complex machining configurations and also to combine LMM with other complementary processes in hybrid manufacturing systems and production lines. The paper presents the development of three generic integration tools for improving the system-level performance of reconfigurable LMM platforms. In particular, the research reports the design and implementation of modular workpiece holding device, automated workpiece setting up routine and automated strategy for multi-axis LMM machining employing rotary stages. An experimental validation of their accuracy, repeatability and reproducibility (ARR) are performed on a representative state-of-art LMM platform. The results demonstrate the flexibility and operability of the proposed tools to address important system-level issues in LMM by creating the necessary pre-requisites for achieving machining ARR better than ±10μm.

Optical emission monitoring for defocusing laser percussion drilling

This paper presents a novel method for controlling the laser-drilling process for a hole by monitoring induced plasma emission. The variation of light brightness from laser-induced plasma is used as an indicator to control laser percussion drilling. Through on-line plasma emission acquisition and analysis, we obtain the positive association between the increased depth and the optical signal output. A coaxial photodiode is used to estimate the brightness levels of laser-induced plasma. The above constitute an inexpensive and practical on-line feedback system that can be easily implemented in the laser systems. All of the processing work is performed in air under standard atmospheric conditions without gas assist. The acquired signal for drilling could also be used as an input to a focus point process control scheme. Moreover, the technology demonstrates the feasibility to develop an automated laser micromachining system. Experimental results show that drilling efficiency was increased 47% by applying the proposed defocusing laser percussion drilling.

Laser manufacturing of microsieves for bioengineering applications

Laser drilling is a noncontact technology which allows high flexibility and full automation of the process. The research presented aimed at developing laser technology for manufacturing microsieves in thin Ni and Al foils. Involute and square distributions of holes were formed with an overall dimension of 3mm. Distance between adjacent holes was 25um to 100um, which meant fabrication of up to 10,000 openings per microsieve. Owing to optimisation of the optical system design and laser micromachining system parameters, holes with a desired diameter of around 12um were fabricated, limited only by diffraction divergence of laser beam. Full Text: PDF References M. Baumeister, T. Scholz, and K. Dickmann, Influence of Mie-scattering on high-speed micro-perforation considering brilliant laser radiation, J. Laser Appl. 22, 48 (2010). CrossRef K. Erkorkmaz et al. Time-optimal trajectory generation for 5-axis on-the-fly laser drilling, CIRP Ann.-Manuf. Techn. 60, 411 (2011). CrossRef M. Baumeister et al. Laser-Mikroperforation ?on-the-fly?: Faserlaser ermoglichen Porengrose CrossRef L. Li, D.K.Y. Low, M. Ghoreshi, J.R. Crookall, Hole Taper Characterisation and Control in Laser Percussion Drilling, CIRP Ann.-Manuf. Techn. 51, 153 (2002). CrossRef

The laser micro-machining system for diamond anvil cell experiments and general precision machining applications at the High Pressure Collaborative Access Team.

We have designed and constructed a new system for micro-machining parts and sample assemblies used for diamond anvil cells and general user operations at the High Pressure Collaborative Access Team, sector 16 of the Advanced Photon Source. The new micro-machining system uses a pulsed laser of 400 ps pulse duration, ablating various materials without thermal melting, thus leaving a clean edge. With optics designed for a tight focus, the system can machine holes any size larger than 3 μm in diameter. Unlike a standard electrical discharge machining drill, the new laser system allows micro-machining of non-conductive materials such as: amorphous boron and silicon carbide gaskets, diamond, oxides, and other materials including organic materials such as polyimide films (i.e., Kapton). An important feature of the new system is the use of gas-tight or gas-flow environmental chambers which allow the laser micro-machining to be done in a controlled (e.g., inert gas) atmosphere to prevent oxidation and other chemical reactions in air sensitive materials. The gas-tight workpiece enclosure is also useful for machining materials with known health risks (e.g., beryllium). Specialized control software with a graphical interface enables micro-machining of custom 2D and 3D shapes. The laser-machining system was designed in a Class 1 laser enclosure, i.e., it includes laser safety interlocks and computer controls and allows for routine operation. Though initially designed mainly for machining of the diamond anvil cell gaskets, the laser-machining system has since found many other micro-machining applications, several of which are presented here.

CPE: Novel method to shorten the lead time for laser micro-machining

Abstract Conceptual profit engines method is a novel design approach to shorten preparation and manufacturing times from the perspective of enterprise objectives. It illustrates conceptual steps of design operation for knowledge-based laser micro-machining information system and provides new insights into decision-making systems with reducing human interaction. This method facilitated laser micro-machining by setting unknown parameters, and it reduced the process time to 47 % with actively reducing operations preventing complex decisions.

Design of Micromachining System Based on Nanosecond Pulsed Laser

In recent years, pulsed laser processing technology is widely used in MEMS device manufacturing, aerospace technology, precision instrument manufacturing and circuit board processing. According to the characteristics of nanosecond laser, this paper designs a novel nanosecond pulsed laser micromachining system with PMAC card as its core unit. The system can achieve automation control of laser parameters and movement pattern of motion system by software, which can easily realize automatic processing of point, line, and plane structure in micron scale. In this paper, several groups of experiments are taken to test the reliability and accuracy of the machining system and find the group to obtain the best processing result.

Microstructuring of electrospun mats employing femtosecond laser

Electrospun mats from nano/micro-fibers with control porosity and pore shape may be ideal candidate for tissue engineering scaffolds. In this study three type of poly(vinyl alcohol) (PVA) mats of 48-65 µm thickness with different nano/micro-fibers diameters mostly of 100-200 nm were deposited by electrospinning process. Controlled density porosity in the electrospun mats was introduced by Yb:KGW femtosecond laser micromachining system. The influence of electrospun mat micro structure, the distance between the adjacent laser ablation points, the number of femtosecond laser pulses on quality and structure of laser irradiated holes were investigated. It was demonstrated that the quality of irradiated holes depend on structure of electrospun mats (diameter of nano/micro-fibers, thickness of mats) and femtosecond laser processing parameters. Varying the distance between points and number of applied femtosecond laser pulses it is possible to fabricate electrospun mats with pores of 22-36 μm diameter.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.10249

Improvement of the Fabrication Accuracy of Fiber Tip Microoptical Components via Mode Field Expansion

A novel method to overcome the problem of accurately centering microoptical components built by direct laser writing on the tip of a single mode optical fiber is presented, and it includes employing mode field expansion. A hybrid microoptical component consisting of an aspherical and a conical lens integrated into a single monolithic element has been fabricated at the end-face of a fiber using the technique of direct laser writing of photopolymers. The optical performance of the fabricated microstructures has been measured experimentally. We show that optical properties of Gaussian and Bessel beams can be easily tuned by adjusting the geometrical parameters of fiber-tip microoptical elements. In addition, we experimentally demonstrate the increase of propagation distance of a Bessel beam five-fold, using the fabricated microoptical element. This improvement in the fabrication method of fiber-tip microoptical elements can be used in the manufacturing of integrated micro-optical devices for optical tweezing, laser micromachining and long focal depth optical systems.

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Fluorescence of silicon nanoparticles prepared by nanosecond pulsed laser

A pulsed laser fabrication method is used to prepare fluorescent microstructures on silicon substrates in this paper. A 355 nm nanosecond pulsed laser micromachining system was designed, and the performance was verified and optimized. Fluorescence microscopy was used to analyze the photoluminescence of the microstructures which were formed using the pulsed laser processing technique. Photoluminescence spectra of the microstructure reveal a peak emission around 500 nm, from 370 nm laser irradiation. The light intensity also shows an exponential decay with irradiation time, which is similar to attenuation processes seen in porous silicon. The surface morphology and chemical composition of the microstructure in the fabricated region was also analyzed with multifunction scanning electron microscopy. Spherical particles are produced with diameters around 100 nm. The structure is compared with porous silicon. It is likely that these nanoparticles act as luminescence recombination centers on the silicon surface. The small diameter of the particles modifies the band gap of silicon by quantum confinement effects. Electron-hole pairs recombine and the fluorescence emission shifts into the visible range. The chemical elements of the processed region are also changed during the interaction between laser and silicon. Oxidation and carbonization play an important role in the enhancement of fluorescence emission.

Electrochemical behavior of a laser microstructured fluorine doped tin oxide anode layer with a plasma pretreatment for 3D battery systems

Fluorine-doped tin oxide (FTO) films with a thickness of about 3 micrometers were prepared by electron cyclotron resonance-metal organic chemical vapor deposition (ECR-MOCVD) under 800 W of microwave power, with tetra-methyl tin (TMT) as a tin precursor. The dome-shaped micro-patterned FTO layer was prepared on a copper current collector using a KrF excimer laser micromachining system for application as an anode for 3D lithium-ion batteries. Mild ECR plasma treatment at 600 W was carried out on the surface of the microstructured FTO anode, and the electrochemical characteristics were investigated with regard to the plasma treatment effects. The results show that physical properties such as the smooth and dense surface morphology and reduced surface oxygen functional groups of the plasma-treated samples enhanced the specific capacity, rate capability, and capacity fading. This was probably due to the reduction of side reactions, which may be closely related to the plasma treatment of the microstructured FTO layer. The ECR plasma treatment plays an important role in reducing the charging transfer resistance. In the experimental range studied, a higher specific capacity of 1425 mA h g−1 at a current density of 117 mA g−1 was observed, with capacity fading of 37.8% after 100 cycles for the plasma-treated microstructured FTO anode.

Stainless Steel Pinholes for Fast Fabrication of High-Performance Microchip Electrophoresis Devices by CO2 Laser Ablation

With the introduction of hobby laser engravers/cutters, the use of CO2 laser micromachining on poly(methyl methacrylate) (PMMA) has the potential for flexible, low cost, rapid prototyping of microfluidic devices. Unfortunately, the feature size created by most entry-level CO2 laser micromachining systems is too large to become a functional tool in analytical microfluidics. In this paper, we report a novel method to reduce the feature size of microchannels and the bulges formed at the rim of the channel during CO2 laser micromachining by passing the laser beam through a stainless steel pinhole. Without the pinhole, the channel width was typically 300 μm wide. However, when 50 or 35 μm diameter pinholes were used, channel widths of 60 and 25 μm, respectively, could be obtained. The height of the bulge deposited directly next to the channel was reduced to less than 0.8 μm with the pinhole during ablation. Separations of fluorescent dyes on devices ablated with and without the pinhole were compared. On devices fabricated with the pinhole, the number of theoretical plates/m was 2.2-fold higher compared to devices fabricated without the pinhole, and efficiencies comparable to embossed PMMA and laser ablated glass chips were obtained. A mass-produced commercial hobby laser (retailing at ∼$2500), when equipped with a $500 pinhole, represents a rapid and low-cost approach to the rapid fabrication of rigid plastic microchips including the narrow microchannels required for microchip electrophoresis.

Femtosecond Laser Micromachining of SiC Ceramic Structures

Femtosecond laser micromachining technology shows abroad application background in the field of micro manufacturing due to its unique advantages, especially for micromachining of ultrahard materials such as Silicon carbide (SiC) ceramic. The femtosecond laser micromachining system was set up, by using the system, effects of scanning velocity and laser pulse energy on quality of micromachined features were evaluated. The optimized technological parameter was obtained as 8mW, 1mm/s with 1kHz repetition frequency respectively on the basis of the morphological characteristics and microstructure accuracy. Besides, V-shaped cavity of 300μm depth and 120°angle was generated with layer-by-layer scan machining. Thus femtosecond laser micromachining technology is an effective method for hard and brittle materials precision processing.

Modeling pulsed laser micromachining of micro geometries using machine-learning techniques

A wide range of opportunities are emerging in the micro-system technology sector for laser micro-machining systems, because they are capable of processing various types of materials with micro-scale precision. However, few process datasets and machine-learning techniques are optimized for this industrial task. This study describes the process parameters of micro-laser milling and their influence on the final features of the microshapes that are produced. It also identifies the most accurate machine-learning technique for the modelization of this multivariable process. It examines the capabilities of laser micro-machining by performing experiments on hardened steel with a pulsed Nd:YAG laser. Arrays of micro-channels were manufactured using various scanning speeds, pulse intensities and pulse frequencies. The results are presented in terms of the main industrial requirements for any manufactured good: dimensional accuracy (in our case, depth and width of the channels), surface roughness and material removal rate (which is a measure of the productivity of the process). Different machine-learning techniques were then tested on the datasets to build highly accurate models for each output variable. The selected techniques were: k-Nearest Neighbours, neural networks, decision trees and linear regression models. Our analysis of the correlation coefficients and the mean absolute error of all the generated models show that neural networks are better at modelling channel depth and that decision trees are better at modelling material removal rate; both techniques were similar for width and surface roughness. In general, these two techniques show better accuracy than the other two models. The work concludes that decision trees should be used, if information on input parameter relations is sought, while neural networks are suitable when the dimensional accuracy of the workpiece is the main industrial requirement. Extensive datasets are necessary for this industrial task, to provide reliable AI models due to the high rates of noise, especially for some outputs such as roughness.

Fabrication of hexagonally arrayed micro-structures with axially symmetrical surface profile by tri-axial excimer laser scanning

This paper presents an excimer laser contour scanning method for achieving hexagonally arrayed micro-structures with an axially symmetrical surface profile. It utilizes a specially designed contour mask for projected laser scanning along three different directions separated by 120° on the surface of a sample. Through rigorous analysis, a new contour mask design method is proposed which guarantees not only the profile accuracy but also the axial-symmetry of machined micro-structures. Experiments have been carried out using a 248nm KrF excimer laser micromachining system. Hexagonal arrays of micro-lenses with an aperture size of 100μm in diameter and a maximum sag height from 15 to 30μm are successfully produced using designed contour masks. The machined profile accuracy is better than ±0.5μm within most of the central area of lens aperture. The flexibility on machined surface profile and its machining accuracy allow new types of micro-lens arrays with specific optical functions and new applications in the future.

三波长同轴输出皮秒激光精细加工系统的研制及其应用

三波长同轴输出皮秒激光精细加工系统的研制及其应用

Femtosecond Laser Micromachining of High Quality Groove on Sapphire Surface

In this paper, high quality grooves were fabricated by femtosecond laser pulse on sapphire surface. Grooves were fabricated under different experimental conditions. The lateral and vertical machining precision was evaluated by scanning electron microscopy and profilometer. High quality grooves could be obtained at the condition of low pulse energy, high scanning-speed and increasing the number of laser scans. The relationship between the width and depth of the groove and the key parameters of femtosecond laser micromachining system was studied. Several samples of the high quality grooves were obtained by femtosecond laser pulses. High quality grooves have a potential application of the fabrication of sapphire-based devices.